Free Below Mercury by Mark Anson

Mercury’s closest approach to the Sun. The orbit insertion manoeuvre takes you over the North Pole, and into a standard polar orbit.’
    Rawlings zoomed in closer on the display, and the tiny dot of Mercury expanded until it became a grey globe. A graphic of a space tug appeared at the end of the green line, moving against the background of the stars. The mission team watched as the tug fired its engine, slowing down and moving into a circular orbit around Mercury.
    Clare leaned forward. The tiny aircraft-shape attached to the front of the tug occupied her full attention.
    ‘Just a moment,’ she said.
    Rawlings halted the animation.
    ‘What kind of ship are we going down to the surface in?’ She pointed at the screen.
    ‘You’re going to be flying one of the Martian spaceplanes – most likely a modified Olympus two-forty,’ Rawlings said quickly, glancing towards the back of the room. ‘We had one back from Mars last month that needed a major overhaul. We’ve bumped it up the priority list, and it’ll be refitted for the mission.’
    ‘You’ve got to be kidding.’ Clare shook her head in disbelief. ‘Why are we taking a spaceplane down to Mercury? Why can’t we use one of the crew shuttles?’
    ‘Because we don’t know what state the landing pad is in after the refinery explosion,’ Helligan’s drawl cut in from behind her. ‘If the pad’s been put out of action by the explosion, a shuttlecraft won’t be able to land.’
    Clare started to speak, but Helligan waved a hand dismissively, and continued: ‘Look, shuttlecraft are designed for landing on flat, concrete pads; they’re not able to land on crater floors. And they don’t have the radiation shielding for an extended stay on the surface. Those spaceplanes are built to operate off dirt strips on Mars – they can take hard landings on rough terrain, and they’ve got plenty of shielding. It’s a safer option.’
    Clare subsided for the moment. Helligan had a point. If they had to land on the uneven terrain of a crater floor, she would rather be in the spaceplane. Still, it was a big, heavy craft to haul all the way to Mercury.
    ‘What about living space when we’re on the surface? We might be there for some time,’ she asked.
    ‘Inflatable Mars habitat modules, carried in the spaceplane’s cargo bay,’ Rawlings answered. ‘The spaceplane can supply all the power and air you need to run them while you’re there. The habitats have adequate radiation shielding for your stay, but you’ll have to retreat into the spaceplane if there’s a major solar event. In the most extreme cases, you may need to take shelter in the mine itself.’
    Clare nodded as she made a note in her pad. They seemed to have thought it all out.
    Rawlings was looking at her, as if waiting to see if she had more objections. She nodded for him to continue.
    Rawlings turned back to the display behind him, and restarted the animation from where the space tug entered orbit round Mercury.
    ‘Your orbit takes you directly over the South Pole, every ninety-six minutes,’ he continued. ‘Now, for the landing, you’ve got to make a special manoeuvre.’
    The animation showed the spaceplane undocking from the tug, and nosing round to latch onto a large, torpedo-like fuel tank, before starting its descent.
    ‘This drop tank provides the spaceplane with extra fuel for the mission, as there will be no refuelling facilities on the surface. The drop tank is jettisoned shortly after the de-orbit burn.’
    On the display, the empty tank fell away from the spaceplane. The display zoomed in further, following the craft as it fell out of the black sky toward the spreading landscape below.
    ‘Even with this extra fuel, making a descent to the surface and returning to orbit again is right on the limits for the mission. There is very little margin for error. You will be carrying a heavy load of fuel and equipment, which will limit your hover time over the surface before you have to